One common approach taken for the purpose of preventing adhesion and bond between a substrate such as paper, converted paper or plastic film and a pressure-sensitive adhesive material is to apply a curable silicone composition onto the substrate surface and cure the coating with heat, UV or electron beams. The coated substrate is generally known as a release sheet.
The composition from which a releasable cured film is formed is required to cure at a low temperature and within a short time from the standpoints of productivity and energy saving and also in consideration of its application to less heat resistant substrates. Especially from the standpoint of preventing the substrate from deforming by heat, it is advantageous to cure a coating with radiation such as electron beams or ultraviolet rays into a cured film.
One useful method for preparing a composition for forming a releasable cured film is to cure an organopolysiloxane having (meth)acrylate groups by irradiating electron beams. The release of a cured film from a tacky material depends on the (meth)acrylate group content of the (meth)acrylate group-containing organopolysiloxane. The cured film requires a greater peeling force as the content of (meth)acrylate groups increases.
On the other hand, at least a certain amount of (meth)acrylate groups is necessary in order to quickly form a cured film. No cured film can be formed if the (meth)acrylate group content is reduced. Also, (meth)acrylate groups contribute to the phenomenon that a cured film firmly bonds to the substrate. An organopolysiloxane having a reduced (meth)acrylate group content cannot form a releasable film on the substrate because the cured film will readily separate from the substrate.
As understood from the foregoing, the releasable cured film involves contradictory release, cure, and substrate bond behaviors. It is difficult to find a compromise between light peeling and formation of a satisfactory cured film.
JP-A 7-316517 discloses that a cured film ensuring light peeling and age stability is obtainable by mixing an organopolysiloxane having (meth)acrylate groups with a non-reactive organopolysiloxane. In this cured film, however, the non-reactive organopolysiloxane which has not been incorporated in the crosslinked structure migrates from the surface of the cured film to a surface in contact therewith, detracting from the residual bonding force and ball tack, that is, the tack of a self-adhesive layer.